This invention relates to hot blast stoves which provide the continuous blast of hot air to a blast furnace in the iron making process. More specifically, the invention is an improved process by which to erect the refractory interior of such a stove.
Typically, there are three stoves to supply the hot blast to a blast furnace. The stoves are tall steel cylinders, lined with brick and nearly filled with a type of brick called checkerwork. The checker bricks store heat produced by burning by-product gas from the furnace. The hot gas passes through the many small passageways in the checker bricks until they are thoroughly heated. Then combustion is stopped and a blast of ambient clean air is blown through the stove, picking up the heat from the checkerwork to make the hot blast for the furnace. The stoves are alternately cycled in this manner, one "on blast" while another is "on gas" so there is always a continuous hot blast for the furnace. A hot blast stove includes as principal parts a shell, combustion chamber, checkerwork, and control valves and lines to regulate and carry the various gases.
The shell is a welded steel jacket, 20-30 feet in diameter, domed at the top, and usually 100-150 feet high. The shell houses the combustion chamber and the checker chamber. A shell must be designed not only to support the brick structure inside, but to withstand the 30-50 psig blast pressure. The shell is insulated from the brickwork to avoid structural damage from the heat and to prevent loss of heat to the atmosphere.
The combustion chamber is constructed of brick with an inner "skinwall" that is free to expand and contract in response to temperature changes. The combustion chamber must be designed to occupy as little of the stove interior as possible and still provide proper flow mixing and combustion of gases.
The checker chamber is completely filled with checker bricks, which have many small, in-line holes (flues) where heat is transferred to and from the gas. Modern checkerwork consists of bricks with many small flues, whereas older checkerwork had to have larger openings to minimize clogging from the action of dirty furnace gas. Improved gas cleaning and more stable brick materials have made possible the small openings which expose a maximum surface area to the gas. Within the checkerwork, different qualities of brick material are used in the several vertical zones where heat, chemical action and structural requirements vary.
Normal stove operation consists of two cycles:
"On Gas"--when the checkerwork is receiving heat from burning furnace gas, and "On Blast"--when the checkerwork is giving up heat to make the hot blast. A stove that is heated but not being utilized for the hot blast is said to be "bottled".
A blast furnace plant runs continuously for an extended period, typically five to seven years, after which it is shut down for maintenance and rebuilding as necessary. During such shutdowns, the stoves are gutted of refractory lining and checkerwork and are relined with brickwork and restacked with checkerwork. This has been done in the past by sequentially performing the relining of the combustion chamber, then of the checker chamber, then laying up of checkerwork. The prior art method might be characterized as a single crew performing the several operations in series.
By the process of this invention, the three major rebuild procedures are performed simultaneously by a safer operation for an improved result with less material breakage, and all at a great reduction in expensive downtime. The new method might be characterized as several crews performing the several operations in parallel.
Briefly, the process of this invention can be summarized as:
A process of erecting interior combustion and checker chambers in a hot blast stove by lining the checker chamber and building the chamber wall from a vertically movable scaffold in the checker chamber shaped to conform with the interior thereof, laying up checkerwork in the checker chamber beneath the movable scaffold, these two operations being supplied from outside the stove through feed openings at progressive heights, and lining the combustion chamber from a vertically movable work scaffold within the combustion chamber. All three principal operations are carried on concurrently.
The details and benefits of the present invention will now be more specifically described with reference to the accompanying drawing.